Ah Puch is the Mayan god associated with death and war, ruling the lowest layer of the Mayan underworld, known as Hunhau. He is akin to Hunhau and Kisin.
When Ah Puch is pictured, he's usually seen with a large body with decaying flesh - his head being a skull or he might holding a skull with a necklace made with eyeballs around his neck or twisted into his hair. He's shown with bells and various symbols of death, such as the vulture, owl or dog.
Even though he is called Ah Puch by Mayan historians, it does not seem to be a valid name for the deity itself.